Correct format() in source-code-variable.css

This is required to let browsers that don’t support variable
fonts (e.g. Firefox on Windows 8) avoid downloading them and fall back
to something usable.

Signed-off-by: Anders Kaseorg <andersk@mit.edu>

Author: andersk

source-code-variable.css

@@ -3,17 +3,17 @@
     font-weight: 200 900;
     font-style: normal;
     font-stretch: normal;
-    src: url('./WOFF2/VAR/SourceCodeVariable-Roman.ttf.woff2') format('woff2'),
-         url('./WOFF/VAR/SourceCodeVariable-Roman.ttf.woff') format('woff'),
-         url('./VAR/SourceCodeVariable-Roman.ttf') format('truetype');
+    src: url('./WOFF2/VAR/SourceCodeVariable-Roman.ttf.woff2') format('woff2-variations'),
+         url('./WOFF/VAR/SourceCodeVariable-Roman.ttf.woff') format('woff-variations'),
+         url('./VAR/SourceCodeVariable-Roman.ttf') format('truetype-variations');
 }
 
 @font-face{
     font-family: 'Source Code Variable';
     font-weight: 200 900;
     font-style: italic;
     font-stretch: normal;
-    src: url('./WOFF2/VAR/SourceCodeVariable-Italic.ttf.woff2') format('woff2'),
-         url('./WOFF/VAR/SourceCodeVariable-Italic.ttf.woff') format('woff'),
-         url('./VAR/SourceCodeVariable-Italic.ttf') format('truetype');
+    src: url('./WOFF2/VAR/SourceCodeVariable-Italic.ttf.woff2') format('woff2-variations'),
+         url('./WOFF/VAR/SourceCodeVariable-Italic.ttf.woff') format('woff-variations'),
+         url('./VAR/SourceCodeVariable-Italic.ttf') format('truetype-variations');
 }